1. Cross-Reference to Related Applications
The present invention is related to the subject matter of the following commonly assigned co-pending application Ser. No. 07/267,713 filed Nov. 4, 1988, which is a continuation of application Ser. No. 06/928,170 filed Nov. 6, 1986 and entitled "Control System For ophthalmic Surgical Instruments."
The present invention is related to the subject matter of the following commonly assigned applications being filed concurrently on even date herewith:
Application Ser. No. 07/428,232 entitled "Control System For Ophthalmic Surgical Instruments", now abandoned; PA1 Application Ser. No. 07/428,354 entitled "Control System For Calibrating And Driving Ultrasonic Transducer", now abandoned; PA1 Application Ser. No. 07/427,614 entitled "Remote Control Console For Surgical Control System", now U.S. Pat. No. 5,249,121; PA1 Application Ser. No. 07/428,125 entitled "Vitrectomy Probe", now U.S. Pat. No. 5,047,008; PA1 Application Ser. No. 07/428,216 entitled "Modular Cabinet For Surgical Control Systems", now abandoned; PA1 Application Ser. No. 07/428,355 entitled "Footswitch Assembly With Electrically Engaged Detents", now U.S. Pat. No. 5,091,656; and PA1 Application Ser. No. 07/428,166 entitled "Motorized IV Pole Assembly", now abandoned.
The disclosures of each and every one of the above-referenced applications is hereby incorporated herein by reference.
2. Field of the Invention
The present invention relates in general to pneumatic control circuits and systems for providing controlled levels of pressurized air or vacuum to instruments used during ophthalmic microsurgical procedures, and in particular to improvements in such pneumatic circuits and to a method of modularly constructing such pneumatic circuits within a drawer assembly.
3. Description of Related Art
In the ophthalmic microsurgical arts, a number of different procedures which require pressurized air or vacuum are known. For example, aspiration, that is providing suction via a controlled vacuum level, is used widely for various procedures and with various instruments. Aspiration is used, for example, during the engagement, stripping and removal of residual lens cortical material in extra-capsular cataract extraction and phacoemulsification procedures. Phaco-fragmentation procedures also make use of aspiration. Anterior and posterior vitrectomies also require aspiration for the removal of cut material from the eye, such as vitreous.
Intraocular pressure (IOP) control provides precisely adjusted delivery of filtered air to the eye during posterior ocular pressure procedures. Also, the IOP system can be used to pressurize an irrigation supply of balanced salt solution for the eye during anterior segment procedures. Microscissors are another ophthalmic microsurgical instrument which are often pneumatically driven. Three different scissor drive modes are known today: single cut mode, variable rate cut mode, and proportional cut mode.
While a variety of pneumatic systems are known for providing the appropriate pressurized air or vacuum signals required for the aforementioned microsurgical procedures or instruments, there nevertheless remains an interest in improving the quality of operation of these devices and making such pneumatic control systems (1) more powerful, in terms of the number of functions supported, (2) more accurate in the sense of precisely providing the desired pneumatic pressure or vacuum signals, and (3) easier and simpler to service and/or repair when necessary.
The assignee of the present invention, namely Storz Instrument Co. of St. Louis, Mo. (hereinafter "Storz"), has marketed an ophthalmic microsurgical system under the trademark "DAISY" which is housed in a single control console and which supports all the pneumatic functions described above, except for (1) pressurizing an irrigation supply for anterior segment procedures, and (2) multi-cut scissors mode. It is one object of the present invention to provide all of the foregoing pneumatic functions, including the two last mentioned, in a manner that satisfies the three aforementioned interests.
The DAISY console, a pressure switch is used to monitor the incoming air pressure of the main supply line that provides air to the pneumatic system. The purpose of pressure switch is to detect abnormally low air pressure conditions which can exist, for example, if the hospital air supply pressure falls beneath expected levels or if some other problem interrupts the air supply to the DAISY console. In the DAISY console, this pressure switch is set to trip out at an appropriate level, such as 80 psig. Through experience with the DAISY pneumatic system, it has been found, that under certain transient conditions, namely low but acceptable pressure levels from the hospital supply line when user requests for high vacuum levels are initiated, demand for the pressurized air momentarily outstrips the ability of the hospital line to supply same on account of very brief delays in pressurized air movement. Such transient conditions on occasion cause the pressure switch to indicate that the air pressure is low, at which time the microsurgical console warns the surgeon of the low air supply condition. However, study has shown that such transient conditions, if of sufficiently short duration, are non-hazardous and the surgeon need not be warned or otherwise interrupted. Thus it is an object of the present invention to provide a pneumatic control system which can handle non-hazardous transient air pressure drops, which still recognizing and correctly responding to transient air pressure drops which do indicate that a warning to the surgeon of the low air pressure condition is required or desirable.
With advances in ophthalmic microsurgical techniques, there is increasing interest and need for a highly accurate IOP system which is capable of delivering controlled low pressure air with a minimum amount of pulsations or other variations in pressure. IOP systems typically operate in the range of 0 to 100 mmHg. At these pressure levels, it has not been possible previously, using on/off solenoid control valves, to ramp up air pressure to a desired setting in this range without overshoot. Further, in prior art IOP systems, there is a discernable variation in the output pressure of the IOP system from the desired pressure setting by as much as plus or minus four mmHg or more. Thus, is an object of the present invention to provide an IOP system which uses inexpensive on/off solenoid control valves, and yet still avoids overshoot and minimizes pressure variations from the desired IOP setting.